Superheterodyne receiver fundamentals In a radio receiver, which single stage accepts a radio-frequency (RF) signal at its input and delivers an intermediate-frequency (IF) signal at its output?

Introduction / Context:
This question targets the core concept of the superheterodyne architecture that dominates modern receivers. Understanding which stage translates incoming radio-frequency (RF) signals to a fixed intermediate frequency (IF) is essential for grasping selectivity, image rejection, and overall sensitivity design.

Given Data / Assumptions:

• A conventional superheterodyne receiver is considered.
• Stages present typically include an RF front end, a frequency changer (mixer plus local oscillator), IF amplifiers and filters, a detector (demodulator), and audio stages.
• We assume standard continuous-wave or modulated RF reception.

Concept / Approach:
The superheterodyne method converts the desired RF channel to a constant IF by mixing it with a local oscillator (LO). The mixer output contains sum and difference frequencies. A subsequent IF filter selects the IF component. This translation to a fixed IF allows highly selective, stable filtering and consistent bandwidth across the tuning range.

Step-by-Step Solution:
Identify the stage that performs frequency conversion → the frequency changer (mixer+LO).Note inputs and outputs: RF in, LO in, IF out (desired mixing product).Confirm that demodulator works at IF or baseband, not at RF-to-IF translation.Audio and loudspeaker stages operate after detection and are not frequency-translating blocks.

Verification / Alternative check:
Block diagrams of superheterodyne receivers universally label the mixer/frequency changer between the RF stage and the IF strip. The IF is fixed (e.g., 455 kHz for AM broadcast), enabling standardized narrowband filters.

Why Other Options Are Wrong:

• Loudspeaker and audio amplifier: act on audio, not on RF/IF translation.
• Demodulator: extracts baseband from IF; it does not create IF.
• RF preselector filter: provides selectivity at RF but does not change frequency.

Common Pitfalls:

• Confusing the detector with the mixer; the detector removes the carrier, whereas the mixer shifts frequency.
• Assuming IF is produced by the RF amplifier; it is produced by the mixer.

Final Answer:
Frequency changer (mixer with local oscillator)